In order to treat a bump such as an aneurysm generated in a blood vessel such as an artery, a medical instrument called a microcatheter which includes an elongated tube having a small outer diameter and an inner cavity is first allowed to pass through the blood vessel and guided into the bump. Then, an in-vivo indwelling member is inserted into the bump through the inner cavity of the microcatheter and indwelled therein. Accordingly, the in-vivo indwelling member becomes a physical obstacle against blood flow and a thrombus is formed around the in-vivo indwelling member. As a result, it is possible to reduce the risk of rupture of the bump such as an aneurysm.
Generally, an in-vivo indwelling member is composed of a metal coil. The metal coil is composed of a secondary coil (see FIG. 3, for example) which is formed into a generally linear shape as a whole by further helically winding a primary coil (see FIG. 1(a), for example) which is obtained by forming a metal wire into a coil shape. When the in-vivo indwelling member which is composed of the secondary coil is guided to a bump such as an aneurysm, the form of the secondary coil is released inside a microcatheter and the in-vivo indwelling member is then guided in a linear form. Then, when the in-vivo indwelling member is released from the microcatheter inside the bump, the shape thereof returns to the form of the secondary coil so that the in-vivo indwelling member can remain inside the bump.
On the other hand, a bump has a various shapes such as a spherical shape, an elliptical spherical shape, a bifurcated bump shape, and a shape in which another blood vessel branches from a bump. Among these shapes, a type called a wide neck aneurysm in which the boundary with a parent blood vessel is wide relative to the diameter of the aneurysm has the following problem. Specifically, when indwelling an in-vivo indwelling member that is composed of a metal coil, for example, a general secondary coil having a helical shape as illustrated in FIG. 3, tensile force for the secondary coil to remain inside the aneurysm is weak due to a wide neck opening. Therefore, the secondary coil jumps out into the parent blood vessel and is caused to flow to the periphery by the blood flow, which may cause a serious risk.
Therefore, it is known that, when an in-vivo indwelling member released from a microcatheter has a three-dimensional structure that differs from the secondary coil having a generally linear shape as a whole as described above with respect to such a wide neck aneurysm, the in-vivo indwelling member can firmly remain inside a bump along the shape of the bump, and the risk of deviation of the in-vivo indwelling member is therefore reduced.
There have been proposed various in-vivo indwelling members having a three-dimensional structure as described above and various producing methods thereof. For example, Patent Document 1 describes a method in which a primary coil is wound around a spherical mandrel or inserted into a mold having a spherical inner hollow section to thereby form an in-vivo indwelling member having a spherical three-dimensional structure.
However, in the method described in Patent Document 1, although the in-vivo indwelling member that has a spherical three-dimensional structure as a whole is formed using the linear primary coil, it is difficult to maintain the form as it is and the shape thereof is therefore disadvantageously lost. Further, when inserting the primary coil into the mold having the spherical inner hollow section, the primary coil is inserted only along substantially the same trajectory inside the mold. Therefore, the primary coil is disadvantageously formed only into a shape wound to have a substantially constant outer diameter (for example, see FIG. 11 for reference).